1. Field of the Invention
The present invention relates to an image stabilizing system. More particularly, the present invention relates to an optical apparatus having an image shake correction function, and a control method thereof.
2. Description of the Related Art
Shake acting on a photographic apparatus, such as a camera, often causes image shake and hence degradation of a captured image. Known technologies for reducing the influence of shake include a technology in which camera shake is detected using an angular velocity sensor, and by, for example, moving part of the lenses or shifting the position of a window used to cutout visible images from frames output from an image sensor, and image shake on the surface of the image sensor is reduced. Since angular shake that can be detected by using this technology using an angular velocity sensor has a significant adverse influence on a captured image under most photographing conditions, this technology is provided in various optical apparatuses as an effective image shake correction technology at present.
Under general photographing conditions, since angular shake is a dominant factor for the image shake, high accuracy image shake correction has been realized using the above-described technology. However, in short-distance photography (large-magnification-ratio photographing condition), there is non-negligible image degradation due to shift shake acting on a camera orthogonally relative to the optical axis of the camera, which cannot be detected by using only an angular velocity sensor. For instance, when photographing an object at a close distance of about 20 cm from a camera, or when photographing an object which is at a distance of as large as about 1 m from a camera but using a photographic lens having a very large focal length (for example, 400 mm), actively detecting and correcting for shift shake are performed.
Japanese Patent Laid-Open No. 7-225405 discloses a method in which, by providing an acceleration sensor that detects the acceleration of a camera body, an amount of shift shake is obtained from the second-order integral of the acceleration sensor output, and an amount of angular shake is obtained from the integral of a separately provided angular velocity sensor, whereby correction for shake is performed using a signal which is a combination of these two parameters. However, the output of the acceleration sensor is likely to be affected by a change in the environment such as disturbance noise and temperature especially in the frequency range of hand shake. The influence of these factors of instability is further increased by the second-order-integration operation, thereby making it difficult to realize high-accuracy correction for shift shake.
Japanese Patent Laid-Open No. 2005-114845 discloses a method in which the amount of shift shake is obtained by assuming it to be angular shake having a rotation center at a position away from the camera. This method corrects image shake by obtaining the rotation radius and the angle of the shake using the outputs of an angular velocity sensor and an acceleration sensor provided in the camera. This method allows computing of a rotation radius from the first-order integral of the acceleration sensor output and hence reduces the influence of the above-described factors of instability.
The method of obtaining shift shake using a rotation radius disclosed in Japanese Patent Laid-Open No. 7-225405 requires an accurate rotation radius to be obtained; however, camera shake usually has a plurality of frequency components and the rotation radius changes in accordance with the frequencies in many cases. Hence, it is difficult to realize accurate correction without obtaining the rotation radius corresponding to each of the frequency components. Use of only a rotation radius corresponding to one frequency component may cause the corrections for other frequency components to be inaccurate, whereby much image shake remains uncorrected.
The present invention provides high accuracy correction in an optical apparatus such as a camera having a function of correcting image shake due to shift shake, using an angular velocity sensor and an acceleration sensor, by realizing correction taking into account a plurality of frequency components included in shift shake.